For years the RAF had identified potentially fatal problems with its ageing fleet of Nimrod aircraft, originally designed to follow Soviet submarines over the North Atlantic and now stuffed with sophisticated electronic surveillance devices to watch or listen to the movements of the enemy on the ground.

Yet the RAF board of inquiry into the crash of the Nimrod XV230 in southern Afghanistan on September 2 last year does not apportion blame. It was set up only to identify the likely cause of the crash - though it makes 33 separate recommendations.

Instead it was left to the RAF's most senior officers, in unprecedented moves, to admit blame and identify a catalogue of failures in the way the planes were inspected and maintained.

Risks involved in the potential hazard of fuel passing close to hot pipes taking air from the engine - identified yesterday as the most likely cause of the crash - were "underestimated", Air Chief Marshal Sir Glenn Torpy, head of the RAF, told journalists.

Air Chief Marshal Sir Clive Loader, the country's second most senior RAF officer, delivered a devastating indictment of safety procedures for the Nimrod. Assumptions about the risk of fuel leaks were "incorrect", he said in personal comments included in the board of inquiry report. He also referred to the failure to instal a fire detection and suppression system in the area where the plane first caught fire.

He also referred to the failure to remedy predicted fuel tank overflows. Though Torpy said the Nimrod fleet was "safe to fly", the MoD has agreed to review how checks on the safety and airworthiness of the Nimrods are carried out. It would be headed by a senior QC, the defence secretary, Des Browne, told the Commons.

Despite the confidence expressed yesterday in Nimrod's safety, Torpy also revealed that air-to-air refuelling of the planes had been suspended after a fuel leak on a Nimrod flying over Afghanistan last month. The cause had not yet been found, he said. Yesterday's report did not identify air-to-air refuelling as a cause of last year's crash even though the plane had just concluded such an exercise before it exploded.

The fire on the plane, which quickly spread to its hydraulic system before causing the plane to explode, is likely to have been caused by escaped fuel igniting against a hot pipe close to the fuselage on the aircraft's starboard side. The fuel escaped from two possible sources: a faulty pressure valve or a leaked pipe coupling.

All the Nimrod's crew of 14 died instantaneously at the time of the crash, the board of inquiry said.

Browne told the Commons that "on behalf of the MoD and the RAF, I would like to apologise to the House of Commons and most of all to those who lost their lives and to their families. I am sorry". He added that the MoD was taking steps "to ensure that a similar accident cannot occur again".

Gerald Howarth, Conservative defence spokesman, told Browne that Nimrods of the kind that crashed should have been replaced by a more modern version four years ago. It was "nothing short of a scandal" that a newer version would not be available for another four years he said. The board of inquiry showed "our armed forces are operating at a tempo well in excess of that for which they are resourced".

Willie Rennie, Liberal Democrat defence spokesman, accused the government of changing the ethos of the armed forces from "can do to make do".

Wing Commander Martin Cannard of the Nimrod's 120 squadron, said at RAF Kinloss, Morayshire, where the crashed Nimrod was based, that he and his colleagues still had "every confidence" in the Nimrod.

But Claire Mitchelmore, the widow of Flight Lieutenant Leigh Mitchelmore, who died in the crash, said the crew had died as a result of "a catalogue of errors and an ageing aircraft" which meant that they had been unable to do their job safely.

"It is unacceptable that nearly all military aircraft are ageing ..." she said. "I feel that they were utterly let down by all those they put their trust in." Helen Nicholas, the widow of Flight Lieutenant Gareth Nicholas, said: "The report confirmed our worst fears - that there was nothing that they could have done and it was an accident waiting to happen".

Robert Dicketts the father of Corporal Oliver Dicketts, who also died in the crash, said the government must ensure that troops sent into conflict were properly equipped. Graham Knight said the board of inquiry proved the RAF "betrayed" his son, Ben, one of the Nimrod's crew. "Now everyone knows this someone will have to fall on their sword and I think it will have to be Sir Glenn Torpy," he added.

Andrew Tucker of law firm Irwin Mitchell, which is representing the families, said: "We are delighted that the MoD has taken responsibility for this tragic incident. Had the necessary precautions been taken ... then there is every likelihood that these service personnel would still be alive".

Still flying after 30 years

The Nimrod fleet entered service with the RAF more than 30 years ago, and was due to leave service in 1995 but had to continue flying on operations over Iraq and Afghanistan. Although designed for maritime operations, Nimrods have been used over land since the campaign in Kosovo in the 1990s. Apart from the 1982 Falklands war, Nimrods served in the 1990 and 2003 Gulf wars and were part of Nato's maritime blockade of the Balkans in 2001.

The Nimrod MR2 is used in stealth missions as its jet noise is virtually undetectable by submerged submarines.

Fresh fears about its safety were raised last month after a safety scare over southern Afghanistan. Although the aircraft landed safely and precise details of the problem are not known, experts believe that the circumstances of the scare were similar to those that led to Nimrod XV230 bursting into flames north-west of Kandahar in September last year. Both aircraft were in the process of airborne refuelling.

Defence company Qinetiq published a report on the repair of fuel leaks in the lower wing surfaces of Nimrod aircraft in March 2006 - six months before the disaster that killed 14 British servicemen.

The findings indicated that the team were concerned about the equipment and methods used to identify and repair fuel leaks on the aircraft. Press Association